It is necessary to adjust components of the resonant circuit(s) of an NMR probe to tune the circuit and to match the circuit to the transmission line directed to the respective RF source/sink. In earlier years, this operation might be done in the purest sense of manual intervention, e.g., manually turning a shaft at the base of the probe body to vary a capacitance or displace a tuning paddle. This operation could be an awkward exercise because of the physical distance of the NMR probe (in a magnet bore) remote from the console of the instrument, and more particularly because introduction of each sample for study typically requires a repetition of the procedure. A tune and match operation that is driven by a mechanism is necessary to enable a feedback arrangement, which can be consistent and efficient, as well as the possibility for unattended operation when a large number of samples are to be examined seriatum. Moreover, simple direct mechanical coupling to a circuit component is not desirable for cryogenic NMR probes housed in a vacuum environment and for which thermal isolation of the resonant circuit is a major design goal.
Prior art directed to this problem has employed stepping motors to turn shafts mechanically coupled to capacitors located in the resonant circuit. Modern NMR probes feature a plurality of RF channels and a similar plurality of adjustments. A prior art approach to this matter utilizes a plurality of motors in one to one association with each adjustable component. An example is U.S. Pat. No. 6,204,665, licensed to Varian, Inc.
Another prior approach to remote/automated multiple NMR probe adjustments employed a first motor for rotating a driving gear and a second motor to axially displace the first motor and its driving gear to an axial position wherein a selected driven gear is engaged. A shaft associated with the selected driven gear is coupled to the respective variable component (capacitor) to achieve the desired circuit adjustment. This arrangement is described in U.S. Pat. No. 6,323,647, assigned to Varian, Inc.